FIG. 1 illustrates a prior art metrology or defect review system 10. It includes a rigid structure that carries a sensor (e.g., CCD camera) 12 and a signal collection module such as imaging module 14 (may be optical or charged particle beam optics). The distance between the imaging module 14 and the sample 22 can be 0.1-to few mm or even few cm”. this depend the focal length of the objective lens and the distance from the last lens surface and the substrate, and the imaging module 14 usually has a large objective lens that has a radius that exceeds one centimeter and can be large as 20 cm for highly complex lens. Such as objective lens of DUV lens use in semiconductor inspection or metrology equipment.
The rigid structure includes an equipment structure 16 and an equipment frame 20.
Under the imaging module 14, an XYZ stage 26 holds a sample (a substrate such as a wafer or mask) 22. The XYZ stage 26 moves the sample 22 under the imaging module 14. The XYZ stage 26 is supported by interfacing elements 28 positioned between the XYZ stage and a lower surface of the equipment structure 16.
Signal scattered or reflected from the sample 22 are collected by the imaging module sensed by the sensor 12 digitized and processed by a processor (not shown). Further image processing is performed to resolve the feature dimension or the shape a defect on the sample.
For angstrom-level imaging accuracy, mechanical vibrations between the sample 22 and the imaging module 14 is a great obstacle. The mechanical vibrations originate from:                1. Outside the system 10, from the fab (fabrication factory) floor and/or the ambience, by acoustic waves.        2. Internal to the system 10, due to vibratory elements inside the system, such as stepping motors, power supply coolers, air bearing jitter etc.        
To reduce the effect of vibration, sophisticated vibration isolation is needed (such as vibration insulators 18 located between the equipment structure 16 and the equipment frame 20, as well as a very rigid structure.
The rigid structure is designed in view of the natural frequency of the mechanical elements. It is desired that the natural frequency exceeds 150 Hz. The higher natural frequency of elements will reduce the undesired shift between the imaging modules and the sample. This means that high stiffness of rigid structure and minimum mass of rigid structure is required. It is quite impractical to achieve higher natural frequency of the rigid structures, due to need to create elements that permit motion, and which use mechanical or air bearings to provide this motion. It is also impractical to resolve angstrom-level elements when the samples are not placed in an extremely quiet and stable condition. This is very difficult because the XYZ stage 26 has to move to new target and settle with zero motion.
There is a growing need to provide a robust evaluation system.